American teenager Daisy (Saoirse Ronan) is sent to live with her aunt and cousins for the summer on their remote farm in the English countryside. Defiant and unhappy, city girl Daisy at first refuses to warm to her new rural surroundings. With her aunt engrossed in her role as a peace negotiator, Daisy and her cousins are left to live in an almost utopian setting and she begins to soften towards her new family and friends. However, their perfect summer is blown apart by the sudden outbreak of a war, leaving them isolated and forced to fend for themselves. When they are violently separated they must embark on a terrifying journey in order to get home.